The present invention relates to a method for improving surface properties of a shaped article of vinyl choride-based synthetic resin or, more particularly, to a method for reducing electrostatic charging on the surface of shaped articles of vinyl chloride-based resins.
As is well known, shaped articles of a vinyl chloride-based resin (hereinafter referred to as PVC resin) are remarkably susceptible to the accumulation of static electricity on the surface thereof resulting in several problems of not only the dirtiness of appearance caused by the deposition or clogging of dusts but also the unpleasant influence to the human body by the electric shock with the static electricity accumulated on the surface and the danger of spark discharge as well as noise generation when a gramophone record made of a PVC resin is played.
Various attempts have been made to devise an effective way or method to improve the surface properties of shaped articles of a PVC resin such as gramophone records in order to reduce the electrostatic charge on the surface.
For example, such an anti-static effect is obtained by coating the surface of the article with a surface active agent. This method is advantageous when the anti-static effect is to be obtained instantaneously but is defective in the rather poor durability of the effect as well as the sticky touch of the coated surface which eventually leads to blocking of the shaped articles with each other.
Another way to reduce the electrostatic charge on the surface of a shaped article of PVC resins is to incorporate or blend the resin with an anti-static agent, e.g. surface active agent, before the resin is shaped into the shaped article by molding. This method is satisfactory in the durability of the anti-static effect but the effectiveness is impractically low when the amount of the anti-static agent is limited. When the amount of the anti-static agent is increased to such an extent that a practically significant anti-static effect is obtained, there may also be caused problems of sticky touch on the surface leading to blocking and readiness of staining in addition to the coloring of the surface as well as the detrimental effect on the heat resistance of the shaped article if not to mention the somewhat adverse effect on the workability of the resin per se admixed with the anti-static agent.
On the other hand, it has been recently proposed that the surface of the shaped articles of PVC resins can be rendered more hydrophilic when the surface is subjected to the treatment with or exposure to low temperature plasma so as that the accumulation of static electricity on the surface can be reduced to some extent. This method is, however, unsatisfactory due to the rather low effectiveness and the poor durability of the effect.